endpol(3G)

NAME
     bgnpol, endpol - delimit the vertices of a polygon

FORTRAN 77 SPECIFICATION
     subroutine bgnpol

     subroutine endpol

PARAMETERS
     none

DESCRIPTION
     Vertices specified after bgnpol and before endpol form a single polygon.
     The polygon can have a maximum of 256 vertices.  Use the v subroutine to
     specify a vertex. Self-intersecting polygons (other than four-point
     bowties) may render incorrectly.  If a quadrilateral projects a self-
     intersecting polygon, its rendering will be hardware-specific. The
     Graphics Library only guarantees that pixels outside of the convex hull
     will not be modified.  Also, concave polygons may not render correctly if
     you have not called concav(.TRUE.).

     Between bgnpol and endpol, you can issue only the following Graphics
     Library subroutines:  c, color, cpack, lmbind, lmcolo, lmdef, n, RGBcol,
     t, and v.  Use lmdef and lmbind to respecify only materials and their
     properties.

     By default polygon vertices are forced to the nearest pixel center prior
     to scan conversion.  Polygon accuracy is improved when this coercion is
     defeated with the subpix command.  Subpixel vertex positioning is
     especially important when polygons are scan converted with antialiasing
     enabled (see polysm).

     After endpol, the current graphics position is undefined.

SEE ALSO
     backfa, c, concav, frontf, polymo, polysm, scrsub, setpat, shadem,
     subpix, v

NOTES
     If you want to use the backfa or frontf routines, specify the vertices in
     counter-clockwise order.

     Although calling concav(.TRUE.)  will guarantee that all polygons will be
     drawn correctly, on the IRIS-4D B and G models, the Personal Iris, Iris
     Entry, Indy, XL, XS, XS24, XZ, Elan, and Extreme systems, doing so causes
     performance to be degraded.

     See the section, "2.1.4 Polygons," in the Graphics Library Programming
     Guide for a discussion on the handling of non-coplanar and/or self-
     intersecting polygons.
     On Impact and Infinite Reality lmcolor cannot be called between bgnpol
     and endpol

     On Impact and Infinite Reality concav(.TRUE.) severly hurts performance
     and some non-simple four sided polygons cannot be handled correctly.